APPLIED ENGINEERING TECHNOLOGY NQF LEVEL 4 SEPTEMBER 2011

INSTRUCTIONS AND INFORMATION

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Answer ALL the questions. Read ALL the questions carefully. Number the answers according to the numbering system used in this question paper. Write neatly and legibly. g = 9.81m/s2 QUESTION 1:  MECHANICAL FUNDAMENTALS OF THE ENGINEERING                          INDUSTRY 1.1 Choose a sentence from COLUMN B to match the description in COLUMN A. Write only the letter (A – J) next to the question number (1.1.1 – 1.1.10) in the ANSWER BOOK. COLUMN A              COLUMN B 1.1.1 1.1.2 1.1.3 1.1.4 1.1.5 1.1.6 1.1.7 1.1.8 1.1.9 1.1.10 Cross-belt drive Flexible couplings Pneumatic valves Hydraulic valves Thrust bearings Diverter valves Pinion Wheel Evaporator Dynamic seals A B C D E F G H I J regulates the flow of gases regulates the flow of liquids are used to support axial loads the belt is crossed if the drive pulley   rotates in the opposite direction to the driven  pulley are used when the two shafts to be  joined are not in a straight line with each other directs the fluid in a system to different components uses the cooling action of the  vaporising refrigerant to cool the    inside of the fridge are used where there is relative       motion between surfaces is the small gear is the larger gear (10 × 1)        (10) 1.2 Indicate whether the following statements are TRUE or FALSE. Write only 'true' or 'false' next to the question number (1.1.1 - 1.1.6) in the ANSWER BOOK. 1.2.1 Friction is a force that resists the sliding or rolling motion of one solid object over another. (1) 1.2.2 Matter is anything that occupies space and has weight. (1) 1.2.3 A lubricant is a material such as wood that helps to increase friction. (1) 1.2.4 A bearing is a machine part with a shaft or an axle that does not allow other parts to move or rotate. (1) 1.2.5 Tapered roller bearings can support large radial and axial loads. (1) 1.2.6 Pressure is a force applied over an area. (1) 1.3 A block with a weight of 30 N is at rest on a horizontal plain. A horizontal force of 6 N is necessary to move the block and a horizontal force of 5 N is necessary to keep the block moving at a constant speed. Calculate the following: 1.3.1 Static coefficient of friction (3) 1.3.2 Kinetic coefficient of friction (3) 1.4 A cardboard box of books with a mass of 70 kg requires a horizontal force of 180 N to drag it at a constant speed across a wooden floor. Calculate the following: 1.4.1 The coefficient of friction (4) 1.4.2 The angle of friction (3) 1.4.3 The horizontal force that will be required if a similar box is placed on top of the first one.  (4) [33] QUESTION 2:  ENGINEERING PRACTICES USED TO CONSTRUCT PROTOTYPES 2.1 You are given the task to design a prototype frame for a mountain bike. Using the step-by-step chart given below of a typical design process list at least ONE example of a step you will take, or a question you will ask during the design of a prototype frame for the mountain bike. (Hint: Your design process must consider modern environmental concerns and manufacturing processes).  Write only the answer next to the question number (2.1.1 - 2.1.8) in the ANSWER BOOK.    2.1.1 DESIGN SPECIFICATION/PURPOSE    2.1.2. RECORD INFORMATION AND GENERATE INITIAL DESIGN IDEAS    2.1.3. PREPARE INITIAL DRAWINGS OF DESIGN    2.1.4. GENERATE ACCURATE PROTOTYPE DIMENSIONS TO              SPECIFICATIONS    2.1.5. DEFINE MANUFACTURING PROCESS OF PROTOTYPE    2.1.6. TESTING OF PROTOTYPE    2.1.7. ANALYSE TEST RESULTS    2.1.8. REVIEW DESIGN (10) 2.2 A horizontal beam is 3m long and is supported at the left-hand end and also 2,5m from the left-hand end. The beam carries the following point loads (ignoring the mass of the beam): ·    300N - 1m from the left end ·    400N - 2m from the left end ·    200N – at the right end. 2.2.1 Make a neat sketch of the beam with all the relevant information on it. (7) 2.2.2 Calculate the reactions. (10) 2.2.3 Check by means of the calculation whether the forces are in equilibrium to each other. (3) [30] QUESTION 3: FUNCTIONALLY DEPENDANT MECHANISMS IN PROTOTYPES 3.1 Name the different parts of the hydraulic brake system according to the part numbers (3.1.1 - 3.1.9) shown as in FIGURE 2 below.                                                                                                                                                (9)   3.2 What type of fluid is used in this hydraulic system? (1) 3.3 Explain TWO purposes of lubricating a gearbox. (2) 3.4 If the pressure in a hydraulic system is 20kPa and the diameter of the plunger is 0,2 m: 3.4.1 Find the area of the plunger. (3) 3.4.2 Calculate the force exerted by the plunger in Newton. (3) 3.5 Name FIVE basic components of a hydraulic system. (5) 3.6 Pneumatic cylinders, rotary actuators and air motors provide the force and movement of most pneumatic control systems. Give TWO main sections of a pneumatic system. (2) [25] QUESTION 4: CONTROL SYSTEM INCORPORATED INTO A PROTOTYPE 4.1 Name FOUR basic functions in the execution of any central control system. (4) 4.2 Explain what is meant by an analogue signal and a digital signal. (2) 4.3 What effect does maintenance and down time has on a control system? (2) 4.4 Mention TWO responsibilities of a process operator working with mechanical equipment. (2) 4.5 Name TWO safe work practices when working with mechanical equipment. (2) [12]                                                                                                  TOTAL                 100 MEMORANDUM QUESTION 1: MECHANICAL FUNDAMENTALS OF THE ENGINEERING SYSTEMS 1.1.1 1.1.2 1.1.3 1.1.4 1.1.5 1.1.6 1.1.7 1.1.8 1.1.9 1.1.10 D E A B C F I J G H                                                                                                                                (10x1) (10) 1.2 1.2.1 1.2.2 1.2.3 1.2.4 1.2.5 1.2.6 True False False False True True                                                                                     (6x1)                                                                                                                                                             (6) 1.3 1.3.1 1.3.2  μs = Fs                               √          R      = 6                          √         30                     = 0,2                        √   μk = Fk         R                           √     = 5        30                           √     = 0,167                      √                                                                      (3) (3) 1.4 1.4.1 W = 70 x 9,81     = 686,7 N                           √ Sliding Force P = 180 N = Fμ μ = Fμ       NR                                 √    = 180       686                                 √    = 0,262                              √ (4) 1.4.2 tan Ø = μ                              √           = tan¯¹ μ           = tan¯¹ 0,262               √              = 14,68°                       √ (3) 1.4.3 The Fμ is proportional to the normal pressure and independent of the area of contact and since the normal pressure is doubled the horizontal force will also have to be doubled: that is force required = 2 x 180                                   = 360 N                        √ Or Sliding force required is  Fμ = μ x NR          √                                                          = 0,262 x (2 x 686)       √                                                  = 359,46 N                    √ (4) [33] QUESTION 2: ENGINEERING PRACTICES USED TO CONSTRUCT PROTOTYPES 2.1 2.1.1 2.1.2 2.1.3 2.1.4 2.1.5 2.1.6 2.1.7 2.1.8 DESIGN SPECIFICATION/PURPOSE What is the purpose of the frame required and what improvements are expected/required? Gather information from the expected client on the preferred design and research latest design features RECORD INFORMATION AND GENERATE INITIAL DESIGN IDEAS Construct sketches of new design, select materials and shapes PREPARE INITIAL DRAWINGS OF DESIGN Make scale drawings of chosen design GENERATE ACCURATE PROTOTYPE DIMENSIONS TO SPECIFICATIONS Make calculations and test dimensions chosen for bearing different loads. Include tolerances, manufacturing processes, cross-sectional shapes and material that will safely withstand calculated stresses. DEFINE MANUFACTURING PROCESSES OF PROTOTYPE Detail specific design processes taking cost and environmental risks/threats into account (pollution, ergonomics, labour costs, materials) TESTING OF PROTOTYPE Test the prototype’s ability to withstand expected stresses and forces that may be encountered during use. Apply a safety factor which exceeds the maximum calculated working load. ANALYSE TEST RESULTS Make a scientific analysis of the test results to determine the suitability of the prototype design. REVIEW DESIGN Review the test results and consider cost, environmental and ergonomic factors. Make a scientifically informed decision to re-design or approve the prototype design to inform the production process. Note     1 mark x 8 steps = 8  +  any other 2 marks =10 Marks must be given to any correct or relevant answers. (10) 2.2 2.2.1 2.2.2 2.2.3.                                                                                                     To find the reaction at L take moments about R, clockwise M = anti-clockwise M                          √                           2.5 x L + 0.5 x 200 = 0.5 x 400 + 1.5 x 3009      √                                          2.5L+100=200+450                                                                              2.5L=200+450-100                  √                                                                               550                                 L=  2.5                               √                                 L = 220N                            √                              To find the reaction at R take moments about L, anti-clockwise M = clockwise M                      √                        2.5 x R = 3 x 200 + 2 x 400 + 1 x 300            √                                2.5R=600+800+300                                  √                               2.5R=1700                                               √                                      1700           R=    2.5           R= 680N                                            √                Check:     upward F = downward F                       √                           220 + 680 = 300 + 400 +200                 √                                 900N = 900N                                    √                    (7) (5) (5) (3) [30] QUESTION 3: FUNCTIONALLY DEPENDANT MECHANISMS IN PROTOTYPES 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.1.7 3.1.8 3.1.9 Master Cylinder Fluid Pipes Disc Brake Disc Pads Hub Axle Slave Cylinder Disc Pedal                                                                                                  (9x1) (9) 3.2 Brake fluid (1) 3.3  Remove heat.  Lubricate the moving parts.  Absorb vibration and shock.  Prevent metal to metal contact.                           Any Two correct or relevant answers (2) 3.4 3.4.1 3.4.2 Pressure = 20 kPa, plunger diameter = 0,2m, plunger area =? A = p x d2 ÷ 4                                         √  A = A = p x (0,2)² ÷ 4                             √     = 0,03142 m²                                     √ F = P X A                                             √          F = 20000 X 0,03142                           √    = 628,4 N                                           √ (3) (3) Pump Motor Reservoir Valves Pipes Actuator Fluid                        Any Five correct or relevant answers (5) 3.6 Production system Distribution system Consumption system                       Any Two correct or relevant answers                                (2) [25] QUESTION 4: CONTROL SYSTEM INCORPORATED INTO A PROTOTYPE 4.1 Sensing or information receiving Information storage     Information processing Decision and action                                                                                                                     (4x1) (4) 4.2 Analogue signal – the signal is continuously variable. Digital signal - a signal that varies in steps. (2) 4.3 It could result in long delays and loss of production.  (2) 4.3 Must carry out their tasks in a responsible and mature manner. All work given must be done in an efficient manner. Must take reasonable care of themselves and others. Must report hazardous conditions and accidents.               Any Two correct or relevant answers (2) 4.4 All equipment and processes which can be hazardous to staff or visitors must not be accessible to unauthorised people. Each employee must be trained in every aspect of the equipment that they operate. Each employee must be trained in general safety regulations applicable to the organisation. Machines must be placed so that there is adequate space between them for rapid evacuation in case of fire as well as easy access to fire-fighting equipment. Any Two correct or relevant answers (2) [12] TOTAL 100